You may think that there are more interesting pastimes than fretting about your retirement portfolio. Watching ants, for example, or staring at the rug until you burn a hole in it with your eyes.

There's no shame in that. Fortunately, you can use a target date portfolio and hand the management duties off to a professional. Just be aware that all target-date funds are different, and that ultimately, you're looking for the best returns with the least amount of risk.

Target-date funds are geared toward people who will retire in a particular year — 2020, for example, or 2055. As the target year approaches, managers decrease the fund's stock holdings and increase its bond weightings. Eventually, the fund becomes an income fund, so retirees can get as much dividend and interest income as possible.

Funds that aim at a retirement date far in the future are essentially stock funds. T. Rowe Price Retirement 2055, for example, has 88.8% of its portfolio in stocks, 8.1% in bonds, and the balance in money market securities, or cash.

The rate at which management reduces its stock holdings is called the "glide path." Some funds aim for a slow, gradual glide path, while others take a steeper descent. A slow path is more predictable.

Yet recent retirees also need some exposure to stocks, because they could live another 35 or 40 years. So some asset allocation funds hit their retirement date with a fair hunk of stocks. T. Rowe Price Retirement 2010, for example, has 56.9% of its assets in stocks. American Century Target Maturity 2010 has none of its assets in stocks.

As you might expect, the T. Rowe Price 2010 fund took a big hit in 2008: a 26.7% loss. The American Century 2010 offering gained 6.9%.

What to look for in a target fund:

•Performance. And not just raw performance numbers, but risk-adjusted performance. A fund manager who was 100% in financial-services stocks, for example, would have clobbered the average 2010 fund. But the risk — as evidenced by the unfortunate events of the past two years — would have been far higher than most retirement savers would have wanted.

One way to measure risk-adjusted performance is through the Sharpe ratio, named after Nobel laureate William Sharpe. The higher the ratio, the better the fund's performance, given the risk it takes.

You should also consider how the fund has done in bull and bear markets. You may not want a fund that puts up killer numbers in a bull market but gets killed in a bear market.

•Asset allocation. A fund with a high percentage of stocks has a steep glide path; one with a lower percentage of stocks has a more gradual one.

•Expenses. As always, the goal is to keep as much money as possible for yourself. If you have a $500,000 retirement portfolio and your fund charges 1.5%, you're paying $7,500 a year — enough for a decent new car every three years.

The chart shows the five largest 2020 funds that have five-year records. We chose 2020 funds because they have the most variation in performance and holdings. Here's a brief rundown of how they stack up. The funds' holdings are from Morningstar, the Chicago investment trackers. Performance and risk figures are from Lipper.

We divided the funds' risk and performance stats into fifths, or quintiles — those in the top 20% would be in the top quintile and earn an A grade. Those in the next 20% would earn a B, and so on.

Don't put all your holdings into any one fund. And you might consider staggering your target-date funds, using a 2020 fund for the first stage of retirement and a 2030 fund for your later years. Although these funds aren't perfect, they will give you decent management — and more time to spend on more important things.

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